Anesthesiology

Thoracic Aortic Procedures – Endovascular Thoracic Aortic Repair

What the Anesthesiologist Should Know before the Operative Procedure

Definition of an Endovascular Repair

Endovascular repair of the thoracic aorta (Thoracic Endovascular Repair [TEVAR]) is typically performed by stent graft placement via peripheral arterial cannulation. These have primarily been deployed to repair the thoracoabdominal and descending aorta, but the use of fenestrated stent grafts in the arch and proximal thoracic aorta has also been described.

A hybrid repair for combined arch and proximal descending aortic disease is performed in two stages. After an open debranching procedure for the aortic arch (or “elephant trunk” procedure), which restores flow to major vessels at the aortic arch and/or thoracoabdominal aorta, an endovascular stent graft repair is performed for completion. Randomized trials demonstrated early perioperative survival benefit, with less spinal cord ischemia, respiratory insufficiency, and renal failure, with no long-term survival difference between an open repair and endovascular repair.

Continue Reading

Endovascular stent grafts have been approved by the FDA for use in the descending aorta for aneurysmal repair; the Medtronic Valiant endovascular stent system has been approved for type B dissections. Off-label use has included repair of transections, penetrating aortic ulcers, and acute dissections. Though their use is controversial in this setting, several studies demonstrate excellent perioperative and long-term outcomes for type B dissections, with some advantages in patients with malperfusion syndromes. Open repair in the setting of malperfusion has a high mortality rate; patients with TEVAR showed aorta-specific survival benefits when compared to those receiving medical management.

A patient is a candidate for endovascular repair if the surgeon decides that an adequate seal can be made for the stent graft, which requires proximal and distal “landing zones” in the aorta of approximately 2 to 2.5 cm in length. Contraindications to endovascular repair include large, irregular calcifications or thrombus present in the proposed landing zone. These conditions may impair the graft apposition to the aortic wall.

Femoral and/or iliac vessels without significant stenosis or previous repair should be suitable for introducing the stent graft. The type of stent graft that will be placed depends on the vessel diameter. Ideally, the stent graft should cover the area between the left common carotid artery and the celiac axis. Intra-arterial contrast dye and fluoroscopy are used for insertion and deployment of the stent graft and to ensure exclusion of the aneurysmal sac and patency of branch vessels. Often, if the branch vessels will be covered by the stent graft, a concomitant bypass of that vessel may be performed.

The endovascular stent graft is typically self-deploying. Within the lumen, a balloon with special channels for blood flow is expanded to seal the proximal and distal ends of the stent to the aorta. Despite the presence of these channels, balloon inflation causes transient occlusion of the aorta for approximately 15 to 20 seconds. This may cause a significant increase in afterload and cardiac stress, especially in patients with limited cardiac reserve.

Thoracic aortic aneurysms (TAAs) have a localized vessel diameter that is 50% greater than the normal value, adjusted for age and height. TAAs are relatively uncommon, occurring in only 10.4 per 100,000 adults, and predominately in men over 65 years of age. Enlargement of TAAs may be progressive and unpredictable, resulting in eventual rupture. Thus, TAA progression is followed closely, and elective repair is usually performed when the aneurysm diameter is >5.5 cm.

Older patients with aneurysmal disease often have comorbidities such as hypertension, coronary artery disease, peripheral arterial disease, diabetes, obesity, and/or COPD. However, patients with connective tissue disorders, such as Marfan’s and Ehlers-Danlos, or chronic inflammatory and infectious conditions, may predispose the patient to development of aneurysms and dissections at a younger age. Peripheral vascular disease is also particularly relevant to this procedure, since the presence of severe disease, tortuosity, small size or significant atheroma may preclude or change the planned access route.

An aortic dissection is structural damage to one or more aortic vessel walls that results in the extension of a tear or blood flow into an abnormal space. Common co-morbidities associated with dissection include systemic hypertension, deceleration injury and blunt trauma, connective tissue disorders, cystic medial degeneration, pregnancy, bicuspid aortic valve, and aortic coarctation. Dissection may also be a complication of cardiopulmonary bypass at the site of aortic cannulation, or any area where the aorta has been cross-clamped or incised.

Classification of aortic aneurysms and aortic dissections can be reviewed in the chapter Thoracic Aortic Procedures – Arch and Hemiarch Procedures.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

The risk of delay is continued expansion of the aneurysm or dissection, or development of malperfusion states, particularly if emergent.

Emergent: Endovascular stent grafts may be placed emergently to repair leaking/ruptured thoracoabdominal aortic aneurysms in lieu of an open repair, which is associated with a high mortality rate. Endovascular repair of aortic transection following trauma may be preferred in young patients without evidence of rupture, after other life- and limb-threatening injuries have been treated. Evidence to support stent graft placement in the emergent setting comes primarily from case series, retrospective, and prospective reviews.

Urgent: Urgent endovascular stent grafts have been placed in off-label settings for type B aortic dissections, distal to the arch-descending aorta transition. Usually, there is time to perform definitive aortic imaging via computed tomography (CT) scan, magnetic resonance imaging (MRI), or transesophageal echocardiogram (TEE). These imaging tests confirm the diagnosis and extent of disease, and determine the adequacy of landing zones for the stent graft.

In the setting of a type B dissection, access to the true lumen of the femoral vessels should be confirmed with vascular ultrasound or biplane TEE. TEE may also identify sites of fenestrations between the true and false lumens, which may influence the length of the stent or the total number of stent grafts placed.

Elective: If elective endovascular stent graft placement is planned to repair a stable aneurysm or dissection, patients should be considered at high risk for perioperative cardiac events and further evaluated as undergoing a high-risk (major aortic or vascular) procedure. Thorough preoperative screening, imaging, and testing should be performed (See Preoperative Evaluation).

2. Preoperative evaluation

Patients should be evaluated for complications from the aneurysm or dissection and symptoms associated with diffuse vascular disease and malperfusion. Other common conditions include cerebrovascular and cardiovascular disease, COPD with smoking history, and renal insufficiency.

a. Medically unstable conditions warranting further evaluation

Medically unstable conditions warrant immediate investigation, particularly if there is evidence to suggest involvement of the ascending aorta, which may necessitate an open repair with deep hypothermic circulatory arrest. Symptoms would include acutely worsening angina, indicating coronary artery involvement, or acute neurologic deficits, indicating carotid artery involvement. Evidence of ischemia and lower branch vessel involvement, including the subclavian, celiac, superior mesenteric, and renal arteries, may also require an open approach to repair.

History, physical exam, and diagnostic imaging should evaluate for evidence of compression of surrounding structures, including the trachea, phrenic nerve, and esophagus. A pericardial or pleural effusion may be seen in the context of a type B dissection. Further imaging such as CT, MRI, or TEE may be useful in determining the extent of involvement of surrounding structures by the aneurysm.

b. When delaying surgery may be indicated

Elective surgery may be delayed if further medical optimization of an uncontrolled condition is possible in order to prepare the patient for the operation or the anesthetic. The advantage of an elective repair is that it allows time for a full evaluation of the extent of aneurysm, coexisting cardiac lesions, and progression of vascular disease. Additional testing and imaging assists surgical and anesthetic decision-making in terms of creating a perioperative plan, and proper allocation of needed resources (hybrid operating room, perfusion, cardiac anaesthesia, and neuromonitoring teams, availability of blood products, peripheral access for cardiopulmonary bypass, etc.).

3. What are the implications of co-existing disease on perioperative care?

b. Cardiovascular system

Uncontrolled chronic hypertension should ideally be treated with long-acting beta blockade. This therapy is intended to decrease heart rate and afterload, thereby reducing wall stress on the aneurysm or dissection. After heart rate control is established and hypertension persists, afterload reduction may be continued with ACE inhibition, calcium channel blockade, or alpha 1 antagonism. Afterload reduction should occur after the initiation of beta blockade to avoid a reflex tachycardia. Cardiac evaluation by EKG and/or echocardiography should be performed for risk stratification and possible treatment.

Cardiac stress testing may also be performed if indicated and would change management, but with great caution, since the risk of aneurysm rupture increases with a hypertensive response to exercise. If worsening coronary or valvular disease is suspected, cardiac catheterization in addition to echocardiography may be performed. If revascularization or valve repair/replacement is necessary, concomitant coronary stenting, CABG, or valve repair via minimally invasive methods or median sternotomy can be performed immediately prior to TEVAR.

Perioperative risk reduction strategies should include controlling heart rate and blood pressure to minimize risk of rupture or expansion of the aneurysm while preserving end organ perfusion. Short-acting agents may be used intraoperatively to fine tune hemodynamic.

c. Pulmonary

Delay of elective surgery for treatment of COPD or reactive airway disease with bronchodilators may be indicated if symptoms are uncontrolled. A routine chest X-ray is valuable in evaluating tracheal compression or deviation and may further suggest the presence of chronic parenchymal changes or pulmonary hypertension. It may also be helpful in detecting a concurrent pleural effusion or pneumonia, which may complicate the postoperative course.

If applicable, smoking cessation should be discussed, since smoking is an independent risk factor for vascular disease, postoperative pulmonary complications, and negatively impacts wound healing. Ideally, this counseling should occur two months prior to the procedure.

d. Renal-GI:

Renal function is initially assessed by evaluating history and risk factors and by obtaining a screening metabolic panel. The potential for acute kidney injury is high if pre-existing renal malperfusion or insufficiency is present and the patient will receive a large IV contrast load. Chronic medications such as diuretics, ACE inhibitors, or other medications metabolized by the renal system should be dose reduced or converted to a different class of medications if patients are identified as being high risk for impending renal failure. Intravascular volume should be repleted, if indicated. Metabolic derangements should be investigated and corrected.

Preoperative renal insufficiency may predispose the patient to contrast-induced acute kidney injury (AKI) and acute tubular necrosis. Although contrast-induced injury typically resolves within a few days in patients with normal preoperative function, significant renal injury or failure is more likely in those with preexisting dysfunction.

Judicious fluid management, maintaining cardiac output and renal perfusion, and cautious use of vasoactive medications during the procedure will help to optimize renal function in these compromised patients. There is supportive evidence for pre-treating patients who are at risk for contrast-induced acute kidney injury with preoperative bicarbonate infusion and the antioxidant N-acetyl cysteine before IV contrast load. Diuretics and mannitol have not been proven to be beneficial for renal protection.

e. Neurologic:

The risk of spinal cord ischemia due to TEVAR is estimated at 4-7%, with paraplegia and paraparesis being a catastrophic risk. Spinal cord ischemia and infarction are at least partially attributed to temporary or permanent occlusion of arterial collaterals that supply the spinal cord by the stent graft. The largest collateral is the arteria magna or artery of Adamkewicz, the name applied to a particularly large segmental artery between T5 and L2; in 95% of patients it occurs between T9-T12, so special consideration should be given to patients having grafts placed in this area.

Other risk factors for spinal cord ischemia include aneurysm extent (from distal to left carotid artery to below renal arteries), open surgical repair, prior distal aortic operations, perioperative hypotension, and iliac artery injury. Early detection and intervention upon spinal cord ischemia is key in preventing progression to infarction; monitoring and management decisions can be altered based on early identification and treatment of high-risk patients.

Pre-existing neurological deficits should be identified preoperatively via a thorough history and neurologic exam; the patient will be examined serially immediately following the procedure. Available neuroimaging and neurovascular imaging should be reviewed. For patients at high risk for spinal cord ischemia and paralysis, intraoperative neuromonitoring and/or lumbar drain placement should be considered. If a lumbar drain is planned, the patient must be appropriately counselled regarding cessation of anticoagulants, according to the most recent ASRA guidelines shown in Table I.

There has been evidence to support use of steroids for spinal cord protection for patients at high risk of spinal cord ischemia. If steroids are selected, methylprednisolone (1000 mg) is typically administered preoperatively; hyperglycemia (glucose target <200) is treated using an insulin infusion. Aggressive perioperative management of perioperative hypotension, low perfusion states, lumbar cerebrospinal fluid drainage and reattachment of segmental arteries have all been demonstrated to help protect against permanent spinal cord injury.

See section VIIa for further discussion about intraoperative management of neuromonitoring and lumbar drain placement.

f. Endocrine:

As with any typical surgical procedure, tight glucose control will promote wound healing and help prevent postoperative infection. Management of thyroid, adrenal, and other endocrine disorders should be maintained as with any general anesthetic. If adrenal suppression is suspected, perioperative stress dose steroids should be considered.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

N/A

4. What are the patient's medications and how should they be managed in the perioperative period?

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Special reminders should be given to patients to continue chronic anti-hypertensive medications and discontinue anticoagulants as appropriate.

The presence of renal insufficiency should prompt a second review of the patient’s medication list, specifically to hold ACE inhibitors, any medication with renal toxicity, active renal metabolites in light of substantial contrast dye load, and potential acute kidney injury risk after TEVAR.

i. What should be recommended with regard to continuation of medications taken chronically?

Chronic use of beta blockers, ACE inhibitors, calcium channel blockers, nitrates, alpha-1 antagonists, and other antihypertensives should be continued. Herbal supplements and over the counter medications containing ephedrine should be stopped, ideally two weeks prior to the procedure.

Anticoagulants should be held according to ASRA guidelines if a lumbar drain is planned (Table I). Herbal supplements known to have anticoagulant properties, such as garlic, ginkgo biloba, ginseng, dong quai, fish oil, and feverfew, should be discontinued ideally 2 weeks prior to the procedure.

The decision to hold anticoagulation should be discussed and managed with the surgical team. Consideration should be given to coexisting disease, weighing the risk/benefit ratio in the presence of drug eluding coronary stents, TIA or ischemic stroke history, presence of mechanical heart valves, etc.

Medications used to manage conditions such as CHF, COPD/asthma, hyperlipidemia, seizures, psychiatric disorders, endocrine disorders, pain, chronic inflammatory states, and immunosuppression should be maintained as for any general anesthetic.

j. How to modify care for patients with known allergies

Contrast dye is used liberally during endovascular stenting, and the patient with contrast dye allergy is of particular concern. In patients with a history of moderate or severe immediate reaction to contrast media, it is common practice to premedicate with corticosteroids, either alone or in combination with antihistamines.

For elective cases, the American College of Radiology recommends:

Prednisone 50 mg by mouth at 13, 7, and 1 hour(s) before contrast injection, along with 50 mg diphenhydramine by mouth OR

Despite premedication, severe anaphylactic reactions have been reported. Therefore, preparation of emergency medications and equipment, as well as continued vigilance, is mandatory before and after the administration of IV contrast in these patients.

Although most devices, Foley catheters, and equipment in the OR are now latex-free, some operating rooms may still contain latex products; therefore, it may be prudent to screen patients for latex allergies preoperatively and ensure a latex-free environment.

l. Does the patient have any antibiotic allergies – Common antibiotic allergies and alternative antibiotics

First generation and second generation cephalosporins are the most studied and most frequently given for the prevention of surgical site infections (SSIs) in cardiac procedures.

Vancomycin is not recommended for routine use due to the limited evidence of efficacy and concerns for increased microbial resistance, and there is no evidence to support its use in institutions with a high prevalence of methicillin resistant staphylococcus aureus (MRSA). Vancomycin is recommended for patients colonized with MRSA, and is often considered for patients with diabetes, immunosuppression, or prolonged hospitalization.

The accepted alternative for patients with penicillin allergies is vancomycin or clindamycin, with addition of aminoglycoside, aztreonam, or fluoroquinolone for gram-negative coverage.

All antibiotics should be redosed according to institutional recommendations and renal function.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

If a patient with malignant hyperthermia (MH) or strong family history of MH is encountered, standard precautions should be taken. Avoid triggering anesthetics such as succinylcholine and inhalational agents, change CO2 absorbent, and flush the circuit with 100% O2 for at least 30 minutes. Ensure availability of emergency equipment and dantrolene if necessary.

5. What laboratory tests should be obtained and has everything been reviewed?

Preoperative blood tests should include a basic metabolic panel with renal function study, baseline complete blood count, and urinalysis. Coagulation studies should be performed to evaluate the patient’s amenability to lumbar drain placement, if applicable, and risk for blood loss and transfusion during surgery. White blood cell count and urinalysis should be performed to screen for infection, which should be treated if found prior to graft placement.

An EKG, chest X-ray, and available cardiac testing or imaging should be reviewed prior to the procedure to evaluate cardiac function.

Upon arrival to the operating room, a pre-induction arterial blood gas should be obtained to establish a baseline, with attention to any aberrancies in acid-base status concerning for malperfusion or pulmonary dysfunction in at-risk patients. An activated clotting time is also useful to establish a baseline value prior to heparinization.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Anesthetic goals

Goals for the intraoperative management of these patients include hemodynamic stability, sufficient oxygen delivery, and adequate volume to support cerebrospinal, cardiac, splanchnic, and renal perfusion. Maintaining body temperature is also important in preventing wound infection and preventing coagulopathy. Tachycardia and hypertension should be avoided, as these increase wall stress and can extend the aneurysm size or dissection.

Patients should be prepared for surgery as if they were undergoing an open repair, since any endovascular aortic repair may be converted to an open repair. With this in mind, fluid warmers, blood products, intravenous access, and equipment to transfuse rapidly should be readily available. A perfusion team and cardiopulmonary bypass circuit should be readily available in case of an emergency. Although neuraxial, regional, and local anesthesia have been described for TEVAR, general anesthesia is the most routinely selected method.

a. General anesthesia

General anesthesia is the most common approach given the utility and value of TEE to evaluate placement of the stent graft for endoleak, and detect catastrophic retrograde dissection. If neuromonitoring is needed to monitor for spinal cord ischemia, somatosensory evoked potentials or motor evoked potentials (MEPs) could be measured. If so, a total IV anesthetic or low-dose inhaled anesthetic is typically used; if MEPs are needed, muscle relaxant may need to be avoided. Adequate large bore peripheral venous access should be placed.

Monitoring should include standard ASA monitors, as well as large bore intravenous or central venous access, with arterial pressure monitoring. Placement of the arterial line should be discussed with the surgical team, with consideration given to the most likely site of endovascular stent placement and goals of monitoring (e.g., choosing a right-sided arterial line may be prudent for systemic blood pressure monitoring if there is a high likelihood of coverage of the left subclavian artery). Bispectral index monitoring and/or cerebral oximetry should be considered if the stent graft will be deployed or have a landing zone near the takeoff of the left carotid artery; however these monitors may be redundant if EEG monitoring is already planned.

In addition to medications needed to induce and maintain general anesthesia, inotropic and vasopressor support, short-acting beta-blockers, calcium channel blockers, and nitrates should be available for rapid hemodynamic control given the potential for lability.

If a patient requires an emergent endovascular repair (or NPO status cannot be verified) or suspected visceral malperfusion, he/she should be assumed to have a full stomach with associated aspiration risk if NPO status cannot be verified. Rapid hemodynamic shifts should be anticipated, identified, and treated when performing a rapid sequence intubation.

b. Regional anesthesia

Although neuraxial techniques have been described for TEVAR, there is an increased risk of epidural hematoma and spinal hemorrhage, as the patient may require heparinization before, during, and after the procedure. If there is an increased risk for spinal cord ischemia and paralysis or a lumbar drain is planned, there would be obvious conflict in choosing an appropriate site for neuraxial blockade in addition to the lumbar drain. In additional, use of neuraxial techniques with local anesthetic will likely cause interference or loss of neuromonitoring signals or postoperative motor and sensory neurologic issues.

Sudden complications or hemodynamic instability that may occur during stent graft placement may necessitate rapid conversion to a general anesthetic, and fluoroscopy equipment (the C arm) may limit access to the patient. For these reasons, the authors prefer a general anesthetic.

c. Monitored anesthesia care

Monitored anesthesia care with local has been described. However, the risk of patient movement during an endovascular stent placement would be potentially disastrous, leading to aneurysm rupture or further dissection of the aorta, should be weighed against the benefit. TEE imaging may be more difficult or impossible, and transthoracic echocardiography would not be able to visualize the descending aorta and arch well. The necessity for monitoring neurologic status, reduced ability to manipulate the bed position in the hybrid operating room, and limited access to the patient given the C arm make MAC less practical.

6. What is the author's preferred method of anesthesia technique and why?

The author’s preferred method of anesthesia is general anesthesia, as above.

a. What prophylactic antibiotics should be administered?

First generation and second generation cephalosporins are the most studied and most frequently given for the prevention of surgical site infections (SSIs).

Vancomycin is not recommended for routine use due to the limited evidence of efficacy and concerns for increased microbial resistance, and there is no evidence to support its use in institutions with a high prevalence of methicillin resistant staphylococcus aureus (MRSA). Vancomycin is recommended for patients colonized with MRSA, and is often considered for patients with diabetes, immunosuppression, or prolonged hospitalization.

The accepted alternative for patients with penicillin allergies is vancomycin or clindamycin, with addition of aminoglycoside, aztreonam, or fluoroquinolone for gram-negative coverage.

All antibiotics should be redosed according to institutional recommendations and renal function.

b. Surgical approaches – What do I need to know?

Simple TEVAR procedures

Patient selection, surgical approach, and indications for thoracic endovascular stent graft repair (TEVAR) are discussed in section I. Early TEVAR cases used extreme measures to ensure a motionless field during stent deployment, including ventricular fibrillation and asystole with adenosine. With the development of the self-deploying stent graft, however, such extreme measures are no longer required.

However, risks of stent graft placement include coverage of branch vessels by the graft, leading to ischemia. Typically, celiac artery coverage is acceptable if a large superior mesenteric artery (SMA) is present and if the right hepatic artery is being replaced or originates from the SMA. Coverage of essential intercostal or collateral arteries that supply the spinal cord may lead to paralysis, although this risk is less than that of an open repair using cross-clamp techniques.

Coverage of the left subclavian artery (LSCA) may be necessary to create up to 2 cm of proximal landing zone, so that the stent graft will seal properly. This is tolerated well in most patients, as the left upper extremity typically has collaterals from the left internal mammary and left vertebral arteries. In this situation, after endovascular stent graft placement, there will be a blood pressure difference of approximately 50 mm Hg between the left and right extremities.

However, there are key indications for revascularization that must be recognized (Table II). If any of these indications are present, revascularization is typically performed via left carotid-to-left subclavian bypass prior to stent graft placement.

If the patient has coexisting distal aortic arch pathology, with more than 2 cm of proximal landing zone distal to the innominate, a right-to-left carotid-carotid bypass may be used to create a proximal landing zone for stent graft seal. If surgically applicable, this would be performed immediately prior to the stent graft portion of the case.

Aortic arch debranching and "hybrid" procedures

Hybrid techniques can create durable repairs in patients with complex aneurysmal anatomy and limited physiological reserve. These procedures minimize physiologic stress and postoperative complications. However, risks for paraplegia, renal insufficiency, and death increase with the visceral portion of the aorta are involved.

An aortic debranching may be performed prior to TEVAR if the aneurysm or dissection involves the mid transverse arch and an adequate proximal landing zone is present. An ascending aortic-arch debranching may be performed prior to endovascular stent graft placement via median sternotomy with cardiopulmonary bypass on standby.

After a partial clamp technique, the proximal ascending aorta is anastomosed to a custom-designed “hybrid antegrade graft,” (Vascutek, USA, Ann Arbor, MI) which debranches the innominate and left common carotid with an antegrade stent graft insertion site across from the aortic arch. Prior to the anastomosis, 100 U/kg heparin is given with a goal ACT of >250 seconds. The debranching graft is then anastomosed to the ascending aorta, left common carotid, and innominate arteries.

Intraoperative EEG and cerebral perfusion monitoring are usually performed during manipulation and grafting of the left common carotid. Prior to the left common carotid anastomosis to the graft, EEG is monitored closely during a five-minute test clamp. If EEG slowing occurs after clamping, perfusion pressure is increased and the test clamp is repeated.

After a successful test clamp, the surgeon completes an end-to-end anastomosis between the graft and the left carotid with subsequent reperfusion. The innominate artery is similarly clamped, anastomosed to the graft, and reperfused in a similar fashion. The TEVAR portion of the procedure can then be completed. Lastly, the antegrade limb of the debranching graft can be oversewn.

A staged approach may be chosen if the aneurysm involves the transverse arch with inadequate proximal landing zone, but acceptable distal landing zone. In the first stage, a total arch replacement (or stage I elephant trunk procedure) is performed to create a proximal landing zone. In this procedure, the three arch vessels are reimplanted into a trifurcated graft in conjunction with an arch replacement using a collared elephant trunk graft (Vascutek USA).

A second stage endovascular repair should then be performed during the same hospitalization as the initial arch replacement. This minimizes the known risk of death from distal aortic complications between stages described with a conventional open second stage repair.

In hybrid procedures, anesthetic goals remain similar to those in TEVAR procedures alone. Again, hemodynamic stability and maintaining end-organ perfusion are imperative. However, fluid requirements may be large, as there is often a significant amount of blood loss. Fluid warmers and forced warm air blankets are crucial to prevent hypothermia.

Concomitant cardiac procedures and TEVAR

Surgically correctable coronary or valvular disease may be present in patients being evaluated for ascending aorta-based arch debranching procedures or first stage total arch replacement. Some centers may perform concomitant cardiac surgery when this occurs. Typically, the cardiac repair is performed first, followed by TEVAR after bypass.

If isolated coronary disease exists, revascularization via coronary stenting or CABG is performed. Surgical techniques include on- or off-pump coronary artery bypass grafting via median sternotomy. Valve procedures may also be performed via median sternotomy or minimally invasive techniques. The right axillary artery may be chosen for cannulation during these procedures to keep the cannula out of the operative field and minimize manipulation of a diseased aortic arch.

Of note, if the LSCA is to be covered by the stent graft, a left carotid-to-subclavian artery bypass or free left internal mammary (LIMA) graft may be necessary to preserve LIMA flow. If an on-pump procedure is planned, the post bypass ACT goal is 250 seconds for the TEVAR portion of the procedure. Surgeons may choose to introduce stent grafts in an ascending valve conduit if the iliofemoral vessels are diseased.

Thoracoabdominal aorta debranching and "hybrid" procedures

Visceral debranching during thoracoabdominal aortic aneurysm repair has also been described. Typically, patients considered for this repair are at high risk for conventional open repair due to significant comorbidities, advanced age, or prior open aortic surgery. Patients may be chosen for visceral debranching and TEVAR to repair visceral button false aneurysm after open thoracoabdominal aortic aneurysm repair: the risk of morbidity and mortality associated with an open repair of this complication is high.

In the case of visceral debranching, moderate hypotension occurs as the visceral segments are reperfused due to central hypovolemia, pooling of blood in reperfused tissues, and vasodilation due to hypoxemia and acidosis after ischemic injury. Initiating measures to attenuate hypotension include discontinuing vasodilators, replenishing intravascular losses, gradually releasing the cross clamp, and initiating short-acting vasopressors. Good communication between the surgeon and anesthesiologist is imperative during release of the cross clamp in these procedures.

c. What can I do intraoperatively to assist the surgeon and optimize patient care?

Maintaining hemodynamic control and end-organ perfusion is the priority of the anesthesiologist during TEVAR. The use of cell saver during hybrid procedures when expected blood loss is substantial may be helpful in reducing a patient’s incidence of transfusion. In addition, real-time monitoring for cardiac ischemia and visualization of stent graft placement via TEE can provide substantial benefit.

TEE is not only a sensitive and specific tool for confirming the diagnosis and extent of the aneurysm or dissection flap, but it can also confirm the placement of the guide wire in the true lumen if an aortic dissection is present. Coexisting pathology that may interfere with sealing of the stent graft, such as other aneurysms, plaques, and calcifications, can also be detected. Changes in systolic and diastolic function, which may occur during endovascular balloon inflation, are easily identified by TEE.

Furthermore, TEE is used to confirm placement and sealing of the endovascular stent graft and detect “endoleaks.” Endoleaks are blood flow outside the stent into the aneurysmal sac or vessel being treated by the graft. An endoleak found after stent graft placement via TEE is classically described as spontaneous echo contrast in the aneurysmal sac or color Doppler flow around the stent. Diagnosis via color Doppler flow is more sensitive than angiography.

The classification of endoleaks is shown below in Table III. The type I endoleak is the most common, representing 24% of all detected endoleaks. These are associated with technical error – misplacement or wrong sizing of the stent – and must be fixed due to continued flow into the aneurysmal sac and continued risk of rupture. This finding usually results in placement of another stent graft for sealing.

Type 2, which is due to flow from a branch vessel, usually resolves spontaneously in 5 to 6 months. Type 3 endoleaks are due to a graft defect. These are typically sealed via the endovascular route by relining the old graft with a covered stent.

Lastly, the catastrophic problem of retrograde dissection after TEVAR may occur in a minority of patients, but the ascending aorta and arch proximal to the stent should be evaluated for dissection and results immediately relayed to the surgical team. Abrupt changes in biventricular function and new wall motion abnormalities may also signal coronary malperfusion, and would be easily identified on TEE.

d. What are the most common intraoperative complications and how can they be avoided/treated?

The most common intraoperative complications include aneurysm rupture or extension of dissection, neurologic injury, including stroke and spinal cord ischemia, cardiac ischemia, visceral ischemia, inadvertent coverage of a branch vessel by the stent, poor stent graft coverage of the aneurysm resulting in an endoleak, and acute kidney injury as a result of dye load and/or ischemic injury. Avoiding and treating these injuries are discussed throughout the text.

e. Positioning specifics and risk of injury

Patients are positioned supine, and a shoulder roll should be placed to extend the neck in cases emergent sternotomy is necessary during the case. The head should be supported due to the risk of neck injury, vertebro-basilar insufficiency, and stroke with extreme extension. We suggest using the visco-elastic gel ring to distribute pressure and reduce the chance of pressure injury.

For optimal surgical access, the arms are padded and tucked to the sides. After securing the arms, the arterial line, pulse oximetry, and functionality of invasive monitors and intravenous access should be verified. EKG leads should be placed at the limbs, avoiding pressure, and should not cross the chest or be placed in unusual locations where EKG tracings may be difficult to interpret. All pressure points should be padded. The urinary catheter should be free of compression or kinking.

The image intensifier and fluoroscopy are integrated into this procedure, and frequent position checks should be performed to ensure that the patient’s head, neck, and shoulders are not compressed by the image intensifier. The anesthesia team should ensure that all central lines, IVs, A lines, Foley catheters, and monitors are secured and protected from accidental snare or loss during movement of the image intensifier.

Cardiac complications: Maintaining hemodynamic stability, sinus rhythm and early identification of ischemic injury to the myocardium via TEE will minimize injury and allow for early intervention.

Pulmonary complications: A major patient care goal is early extubation whenever possible to minimize the risk for postoperative pulmonary complications. Using short-acting anesthetics, narcotics, benzodiazepines, and muscle relaxants while avoiding fluid overload may expedite the process. Early extubation will allow early neurologic postoperative examination.

Neurologic: Although the risk of spinal cord ischemia and subsequent paralysis is reduced with endovascular stent graft placement compared to open repair, the high-risk patient may benefit from early identification and treatment of ischemic changes found on intraoperative neuromonitoring with transcranial motor-evoked potentials (MEPs) or somatosensory-evoked potentials (SSEPs).

Neuromuscular blockade and inhaled anesthetics should be avoided during MEP and SSEP monitoring, as these agents blunt or prevent elicited responses, making interpretation during surgical manipulation impossible. The authors therefore prefer a total IV anesthetic. A neurologist should be involved in the interpretation of neuromonitoring signals intraoperatively. Further, a lumbar drain is recommended in patients with extensive thoracic stent graft placement or previous aortic repair.

Complications of the lumbar drain include meningitis, CSF leak, epidural hematoma, and catheter breakage. If CSF is drained too rapidly, traction on the cerebral bridging veins may result in subarachnoid hemorrhage. To reduce the risk of epidural hematoma and subarachnoid hemorrhage, preoperative anticoagulants should be withheld as outlined in Table I.

At our institution, if a ‘bloody tap’ is encountered during lumbar drain placement, the procedure is aborted, and the surgery is postponed for 24 hours A neurological exam should be repeated over this time period and consistently negative prior to undergoing surgery. If placed successfully, goal CSF pressures during and after the surgery should be 10 to 12 mmHg. If spinal cord ischemia is suspected intraoperatively or postoperatively, CSF pressure goals remain the same, but mean arterial pressure should be maintained at approximately 100 mmHg to increase spinal cord perfusion pressure.

Renal: Maintenance of intravascular volume, renal perfusion pressure, and pre-treatment of patients who are at high risk for acute kidney injury will help prevent poor renal outcomes postoperatively.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

The patient should meet standard extubation criteria, with particular attention to intact neurologic status and following commands, cough/gag reflexes, and appropriate reversal of neuromuscular blockade if used.

c. Postoperative management

1. What analgesic modalities can I implement?

For isolated TEVAR procedures, groin access sites are typically the only incisions, and patients do not have significant referred pain. Postoperative analgesia is frequently managed with intravenous narcotics, acetaminophen, and local anesthetic at the incision site. Non-steroidal anti-inflammatory drugs are avoided in the context of intraoperative intravenous contrast load in order to prevent additional renal injury. Considering the risk from residual heparinization, the presence of a coexisting lumbar drain, and the risk of compromising the neurologic exam, and side effects of hypotension, although it has been described, neuraxial anesthesia is generally not performed postoperatively.

2. What level bed acuity is appropriate?

Although these patients may be extubated immediately postoperatively in the OR, they should routinely go to a level of care that provides frequent neurologic assessments, continued hemodynamic support and maintenance, and management of invasive monitors, such as the lumbar drain. At most centers initial recovery involves an intensive level of care.

3. What are common postoperative complications, and ways to prevent and treat them?

Early mobilization, use of incentive spirometry, early removal of invasive monitors when possible, and DVT prophylaxis are crucial in preventing postoperative complications and prolonged hospitalization.